When you have a panic attack, your body goes into fight or flight mechanism. Aderenaline gets pumping and your body and subconscious prepares for a life or death fight. Or to run away to safety. When a panic attack happens when you're about to pick up the phone, and there's no external threat in your consciousness or surrounding, your body reconciles the fight or flight reaction by deciding you're going to die. This is why you feel like you're going to die. Not sure if this helps, but the feeling of you're going to die is a natural reaction to what's going on in your body.